The present invention relates to a rotary drilling bit for well drilling; and more particularly is related to a new tool to be used with the rotatory drilling method, which presents remarkable differences and advantages over the conventional drilling tools and drills heretofore used.
To provide an idea about the differences and advantages of this new tool, it is considered necessary to describe briefly the drilling bits of the rotatory type which exist in the market.
At present the bits are separated in two big groups, the first one comprising all of those bits which do not have any movable part, which are made from one piece and rotate in an integral form. This type which predominatly scrap or drag the bottom of the well such as the so called "fish tail" bits, wing bits, and diamond bits. With these types the drilling is performed by the rotation and by the application of a determinate weight on the bit in such a manner that the bottom of the well is scraped, and the detritus are drawn into the surface by the circulation of the drilling fluid. These bits are very rarely used at present time, except in very special instances due to the limitations thereof, especially with regard to the drilling of hard formations, principally massive rocks.
The second group relates to bits which have rotating or rolling elements in their lower part; these rolling elements are principally cones with strias or teeth which roll in the bottom of the well by the application of the weight on the bit, the rolling resulting in the crushing of the rock. The crushed formation is drawn into the surface by the circulation of the drilling fluid. The rolling elements in the actual bits always are in a variable number, the more ordinary being those which comprise three cones integrated in only one piece and which can not be disassembled or taken apart and therefore can not be repaired. In fact, the triconical bits are built by manufacturing separately each one of the three cones and its corresponding leg provided with bearings and seals which are individually built, that is each one of the legs is separately built. Then during the manufacturing these three parts are bond by welding, forming a single unit. The bit undergoes a wearing of the teeth of the cones, of the cones themselves, of the seals and of the bearings, and thus after of a certain time, when the failure or the wear of some of these constructive elements occurs, the bit will be totally useless, without the possibility of repairing the result is a large waste of material and work which never can be recuperated. Once some of its elements fail the bit is totally discarded without the possibility of recuperation. Another variation of this type of bit is the so called cross bit which comprises four tooth rollers, cones or rolls arranged in a such manner that two of the rollers are placed along one of the diameters, but without totally cutting the full diameter, only the central part, and the other two rollers are placed at 90.degree. and cut the circumferential part of the well to be drilled. Sometimes these tools were able to be repaired but with a considerable cost, and its efficiency is limited, thus it is very rarely used.
There is another group of drilling bits, known as differential or Zublin bits. These bits are of the single cutting head type, reparable and replaceable, which are up to now practically obsolete because of their poor efficiency and limited use. In fact these bits perform like drag bits because the motion of the cutting heads is rather a wobbling motion instead of a true rolling mechanism. The Zublin simplex bit which has an almost spherical cutting head rotating in an inclined angle of 30 degrees from the vertical produce a scraping and reaming action in an up and down motion combined with some rotation.